Is Cricoid Pressure Showing Cracks?

Cricoid pressure is dead, right? Many have made this claim including a brilliant argument against its use by Dr. John Hinds (https://vimeo.com/96709226). Despite the many eulogies, we continue to hear about cricoid pressure, including in the recent trial in JAMA Surgery: Effect of Cricoid Pressure Compared With a Sham Procedure in the Rapid Sequence induction of Anesthesia.

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Cricoid pressure was first described in the medical literature by Dr. Sellick in the 1960s though similar techniques were described as far back as the 1770s (Sellick 1961). Sellick’s maneuver entails the application of pressure (30 Newtons) over the cricoid cartilage with the thumb and one to two additional fingers.

The goal was to compress the cricoid cartilage against the esophagus in order to occlude the esophagus and prevent regurgitation of stomach contents into the upper airway. Initial studies on the maneuver suffered from a bevy of methodological flaws including small n, lack of blinding or randomization and selection bias. Despite this, Sellick’s maneuver was widely adopted and taught to hordes of anesthesia, critical care and emergency residents.

Studies investigating cricoid pressure in the last decade have demonstrated a number of issues with the claims that it can prevent passive regurgitation. Check out this free chapter on EMRAP for an in depth discussion (https://www.emrap.org/episode/april2015/medicalmyths). Dynamic MRI studies demonstrate that application of pressure to the cricoid cartilage displaces the esophagus laterally instead of occluding it (Smith 2003, Boet 2012). An ultrasound study demonstrated similar findings: In 60% of patients the esophagus was lateral to the airway and cricoid pressure led to displacement rather than occlusion in all patients. (Tsung 2012)

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Additionally, application of cricoid pressure decreases airway patency and increases the chance that your view of the airway will be obscured (Allman 1995, Palmer 2000, Smith 2002, Oh 2013). Finally, no study to date has demonstrated a reduction in aspiration episodes with the application of cricoid pressure. A large observational study of pregnant patients undergoing C-sections found no difference in aspiration events and that the overall aspiration event rate was low (Fenton 2009). However, up until this point, there has not been a high-quality, randomized controlled trial performed.

The IRIS Trial

This was a multicenter, randomized, double-blind, trial attempting to answer the question of whether “sham” cricoid pressure application was non-inferior (defined as < 50% increased aspiration rate, RR < 1.5) to Sellick’s maneuver in terms of reducing pulmonary aspiration. Pulmonary aspiration was defined either as seeing fluid at the level of the glottis during laryngoscopy or by tracheal aspiration after intubation.

Blinding was obtained by placing an opaque cover over the hand of the operator who was randomized either to apply cricoid pressure or not. The researchers looked at a number of secondary endpoints including difficult tracheal intubation, intubation time > 30 seconds, Cormack and Lehane Grade 3 or 4, interruption of cricoid pressure and improvement in view after interruption of cricoid pressure.

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As mentioned in the title, this was not an ED-based study, but rather a study of patients > 18 years of age who were undergoing general anesthesia in the OR with either shortened fasting time or the presence of at least one pulmonary aspiration risk factor (ie BMI > 30, ileum, gastroparesis etc).

Across 10 centers, the study enrolled 3,472 patients (goal sample size n = 3500). The overall aspiration rate was lower (0.55%) than what the authors presumed at the start of the study (2.8% presumed rate) with no significant difference between the two groups (0.6% Sellick’s maneuver group vs. 0.5% in the “sham” group).

The calculated relative risk was 0.90, but had wide confidence intervals (0.33 —2.38) with the upper limit surpassing the non-inferiority limit. Thus, the authors conclude that the trial “failed to demonstrate the non-inferiority of the sham procedure in preventing pulmonary aspiration.”

For a number of secondary endpoints, sham cricoid pressure was superior to Sellick’s maneuver including intubation time < 30 seconds and Cormack and Lehane grade. Interruption of cricoid pressure was significantly higher in the Sellick group and interruption frequently led to an improved view of the cords. The sham maneuver was not worse than Sellick’s maneuver for any of the other secondary endpoint.

IRIS has a number of strengths. It is the first large randomized trial looking at Sellick’s maneuver, randomization and blinding were applied, and the study had no major protocol violations.

There are important limitations to consider: the study was not ED based, pregnant patients were excluded (aspiration is a major cause of morbidity and mortality in this group) as were pediatric patients, 13% of patients had nasogastric tubes prior to intubation and this was not randomized.

Though there was blinding, it’s possible that intubators could have figured out whether cricoid pressure was being applied or not. The biggest issue, though, is that the group massively overestimated the frequency of pulmonary aspiration and because this event was infrequent, the confidence intervals around the point estimate for the relative risk were wide.

As the authors state, this trial is technically a negative study – it does not demonstrate non-inferiority of the “sham” maneuver in comparison to Sellick’s maneuver. However, there is an absence of any hint of benefit to cricoid pressure and a larger study with adequate event estimates would likely have shown this. Additionally, the “sham” procedure clearly outperformed Sellick’s maneuver in terms of quality of view and difficult views with Sellick’s maneuver were improved by removal of cricoid pressure.

Bottom Line

Occlusion of the esophagus by cricoid pressure appears to be a myth based on MRI and US studies. Previous literature demonstrates that cricoid pressure gives inferior views and no high-quality literature has shown decreased aspiration with application of cricoid pressure.

All of this in conjunction with the numbers seen in the IRIS trial tells us that pulmonary aspiration is uncommon in the OR setting and isn’t reduced by the application of Sellick’s maneuver. While an ED based study would be nice to have, the current evidence tells us that application of cricoid pressure is unlikely to benefit our patients but is likely to make our intubation more difficult.

Anand Swaminathan, MD, is an assistant clinical professor of Emergency Medicine St. Joseph’s Hospital in Paterson, NJ. His main interests are in resident education, resuscitation and knowledge translation. He is a deputy editor for EM: RAP, managing editor for EM Abstracts and an associate editor for REBEL EM and REBELCast.

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